Rhizopus Soft Rot on Pear (Pyrus serotina) Caused by Rhizopus stolonifer in Korea

Rhizopus soft rot caused by Rhizopus stolonifer occurred on pears (Pyrus serotina) in the Jinju City Agricultural Products Wholesale Market in Korea from 2004 to 2005. The infection usually started from wounds due to cracking at harvest time. The lesions started as water-soaked, rapidly softened, then gradually expanded. The mycelia grew vigorously on the surface of the fruits and formed stolons. Colonies on potato dextrose agar at 25℃ were white cottony to brownish black. Sporangia were globose, black and 90~120 µm in size. Sporangiophores were light brown and 480~2600 × 12~18 µm in size. Sporangiospores were globose to oval, brownish, streaked, and 8~14 × 6~10 µm in size. Columella were light brownish gray, hemispherical and 70~80 µm in size. On the basis of these symptoms, mycological characteristics and pathogenicity tests on host plants, the fungus was identified as Rhizopus stolonifer (Ehrenb.) Vuill. This is the first report of rhizopus soft rot on pear (P. serotina) caused by R. stolonifer in Korea.